There is known from the prior art, for example, the publication DE 10 2010 064 252 A1. This describes an auxiliary brake system for an at least electrically driven motor vehicle. A first electric machine, which is designed as an electric motor and as a counter-current brake, is used in order to generate additional braking forces in the vehicle. The electrical energy required for this is provided by a second electric machine, which is coupled as a generator brake to an internal combustion engine of the motor vehicle.